The invention relates to methods and apparatus used in the preparation of materials to be used in the fabrication of pneumatic tires. In particular the invention relates to the perforated cylindrical drum portion of a xe2x80x9cFalse Drumxe2x80x9d server on which elastomeric sheet materials are held while being cut prior to being transferred to a tire building drum.
It is known that in making vehicle tires, for example for automobiles, that manufacture of a so-called carcass is first achieved by successively assembling several different components. In other words, the different carcass types included in a production range can be distinguished from one another depending on the presence thereon of the various accessory components and/or the typology of the accessory components themselves. By way of example, when carcasses for tubeless tires are to be produced, that is tires that in use do not require the presence of an inner tube, the main components can be considered to include a so-called inner liner that is a layer of elastomeric air-impervious material, a carcass ply, a pair of annular metal elements, commonly referred to as bead cores, around which the opposite ends of the carcass ply are folded. as well as a pair of sidewalls made of elastomeric material, extending over the carcass ply at laterally opposite positions. The accessory components may in turn comprise of one or more additional carcass plies, one or more reinforcing bands for overlying the carcass ply or plies at the areas turned up around the bead cores (chafer strips), and others.
Certain tire building assembly lines use servers of various kinds for the purpose of securely holding flat materials such as tire innerliner while it is being cut to size. Servers are commonly of the flat conveyor type, such as the one shown in British Patent No. 1,010,597 (Dunlop Rubber Company) or the conveyor and cutting system shown in U.S. Pat. No. 4,722,255 (Choate, et al.), wherein a continuous flat sheet of material is delivered upon a flat conveyor to a cutting knife and then the material is removed to be placed upon the tire being built. Another such conveyor system is taught in U.S. Pat. No. 5,820,726 (Yoshida, et al.), incorporating a xe2x80x9ctransfer drumxe2x80x9d element which feeds material to the conveyor system.
Drum servers, or so called xe2x80x9cFalse Drumxe2x80x9d servers, are an alternative conveyor of flat or sheet tire materials that must be held securely while being cut. After being cut, the sheet material is moved to the tire under construction on the building drum. Generally such a False Drum server consists of a horizontally disposed drum or cylinder that is able to rotate about its cylindrical axis. One particular False Drum type server consists of a circular cylindrical drum that is hollow. The surface of the drum is perforated around most of its circumference, and air is pumped out of the drum in sufficient volume that the low pressure within the drum provides a suction adhering surface which can securely hold the flat or sheet materials that are being cut while being held on the server. When a flat sheet of material, such as tire innerliner, is placed on the perforated cylindrical part of the server, the pressure differential between the inside of the drum and the outside causes the flat material to adhere to the drum surface while the material undergoes a cutting operation.
An alternative drum-type server system which also holds flat materials to its cylindrical surface is taught in U.S. Pat. No. 4,504,337 (Askam, et al.) which describes a drum type server system wherein the method by which the flat materials that are held to be cut are held securely by a magnetic surface. Such a system, however, is of course limited in use to flat or sheet tire materials that contain steel or ferromagnetic elements such as wires, cords or metal cloth.
The type of False Drum server described hereinabove, in which air is drawn through a perforated cylindrical surface as a method by which to hold securely the materials being cut, is suitable for use with nonmagnetic sheet of flat material. Also suitable is the vacuum cup method taught in U.S. Pat. No. 4,891,082 (Broyles and Portalupi) wherein xe2x80x9csets of vacuum cups spaced circumferentiallyxe2x80x9d around the circumference of the outer rim of a xe2x80x9ctransfer rollxe2x80x9d which serves essentially the same purpose as the aforementioned False Drum server. The vacuum cups are pumped individually by compressed air motors.
The suction adhering part of the perforated drum type False Drum server is its perforated cylindrical drum surface. The False Drum server has a substantially bigger diameter than the building drum. Sheet rubber components are measured to a required length on the False Drum server, and then are cut before being transferred to the building drum. The elastomeric sheet or flat materials that are placed on the False Drum server are held to the False Drum server because the pressure differential across the perforated cylindrical surface makes the cylindrical surface into a suction adhering surface.
False Drum servers generally have the advantage being faster than traditional conveyor or belt type (flat) servers or roller conveyors in terms of allowing greater speed of cutting of flat sheet materials. A disadvantage of False Drum servers, however, is that for flat components, such as innerliner and ply, the portion of the perforated cylindrical surface that is not covered by the flat material being cut is open to the free flow of air into the drum. Such free flow of air weakens the pressure differential that holds the sheet material to the drum. (Uncovered holes represent xe2x80x9cleaksxe2x80x9d.) One way to deal with this leakage problem is simply to use adhesive tape or other materials to block the flow of air through those portions of the perforated surface that are not covered by the flat sheet material. (In other wordsxe2x80x94plug the holes.) But since the various pieces of material being cut are often of different sizes from one another, as typically happens when changing from a large tire component to a smaller component, the tape or other air flow blocking material must be removed and replaced so that the low pressure inside the drum can thereby be maintained. (You don""t want holes to be plugged where you want the vacuum-suction to hold material.) However, the time required to place tape over the unused portions of the perforated surface area, and remove it later, is undesirable. Another risk of the tape hole-plugging method is contamination of the tire components with pieces of adhesive tape that might work loose and attach themselves to the sticky uncured elastomeric material.
An alternative to the use of tape is to use a massively over-dimensioned air pump to remove air from inside the False Drum. With a sufficiently high capacity air (vacuum) pump, holes (leaks) become a non-problem. However, oversized pumps are not desirable because of energy consumption and environmental considerations as well as overall capital costs and operating costs. Another solution is proposed in the aforementioned U.S. Pat. No. 4,891,082 (Broyles and Portalupi) which discloses the use of individually controllable vacuum pumps for each vacuum cup used to hold sheet materials on a cylindrical surface. This method requires, however, that complex controls be used to control the individual vacuum pumps to achieve both economy of operation and the ability to provide a suction adhering surface having a size that rapidly accommodates flat sheets having different amounts of surface area of specific flat sheet materials being held by suction forces to the cylindrical surface.
What is needed is a technique for controlling the vacuum to the holes in the surface of a False Drum server, without requiring oversized pumps and/or without requiring a plurality of pumps.
It is an object of the present invention to provide methods and apparatus as defined in one or more of the appended claims and, as such, having the capability of accomplishing one or more of the following subsidiary objects.
According to the invention, method and apparatus are provided for controlling airflow (suction) through (pressure differential across) a plurality of holes (perforations) extending through the outer surface of a cylindrical drum.
According to a one aspect of the invention, two axially movable disc-like baffle plates are provided within the drum, defining a volume therebetween. The baffle plates are axially moveable, and sealingly engage the inner surface of the drum. Their positions determine the effective width (along the axis) of an area of the surface of the drum which will exert suction on a sheet of material laid on the surface of the drum.
According to another aspect of the invention, a circumferentially moveable curved cylinder segment is provided, conforming to the inner surface of the perforated cylindrical drum, and by circumferentially positioning the curved cylinder segment adjacent a portion of the inner surface of the hollow perforated cylindrical drum, the amount of perforated surface area through which air can be drawn into the hollow cylindrical drum can further be controlled.
In this manner, suction can be provided only at selected ones of the perforations which correspond to a desired amount of surface area to be used for holding elastomeric sheet materials on the outer surface of the drum.
An advantage of the present invention is that it provides simplified methods and apparatus by which to control or vary, on the hollow perforated cylindrical drum portion of a False Drum server, the portion of the total perforated surface area through which air can be drawn into the cylindrical drum portion of the False Drum when the entire perforated area is not covered by sheet material being processed.
Another advantage of the present invention is to provide simplified methods and apparatus by which to control or vary, on the perforated drum portion of the False Drum server, the circumferential dimension of the perforated area through which air can be drawn into the perforated drum.
Another advantage of the present invention is to provide simplified methods and apparatus by which to control or vary, on the perforated drum portion of the False Drum server, the axial dimension of the perforated area through which air can be drawn into the perforated drum.
Another advantage of the present invention is to provide simplified methods and apparatus by which to move and otherwise position from outside of the drum various airflow blocking devices placed inside the hollow cylindrical drum.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.